This application is based upon Japanese Patent Application No. 2001-226409, filed on Jul. 26, 2001, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to an exhaust gas heat exchanger for performing heat exchange between exhaust gas generated by combustion and cooling water. Specifically, the present invention relates to an exhaust gas heat exchanger for cooling the exhaust gas in an exhaust gas recirculation system (i.e., EGR system).
2. Related Art
As shown in FIG. 1, an exhaust gas heat exchanger for cooling the exhaust gas in an EGR system (hereinafter, referred to as an EGR gas heat exchanger) is equipped with plural laminated exhaust gas tubes 301 disposed in a tank 302. The exhaust gas tubes 301 penetrate and are attached to a core plate 330. A peripheral portion of the core plate 330 is folded toward the tank 302, and is attached to an outer wall of the tank 302. The tank 302 is closed with the core plate 330 to isolate a cooling water passage formed in the tank 302 from a bonnet 306. A cooling water inlet pipe 304 and a cooling water outlet pipe (not shown) are disposed on the tank 302 to permit the flow of the cooling water through the tank 302.
In this EGR gas heat exchanger, an adequate contact area is necessary for ensuring contact strength between the peripheral portion of the core plate 330 and the tank 302. Therefore, when the core plate 330 is folded toward the tank 302 as shown in FIG. 1, the cooling water inlet pipe 304 must be kept away from the core plate 330, for example, the distance l in the figure is about 20-30 mm, to obtain the adequate contact area between the core plate 330 and the tank 302. As a result, the cooling water becomes stuck at a portion of the tank 302 between the core plate 330 and the cooling water inlet pipe 304 or between another core plate (disposed at the other side, not shown) and the cooling water outlet pipe. Accordingly, the heat exchanging efficiency would be lowered and the boiling of the cooling water may occur at the vicinity of the core plate.
An object of the present invention is to provide an exhaust gas heat exchanger in which a cooling water pipe is disposed close to a core plate to improve the heat exchanging efficiency and resistance to boiling.
The exhaust gas heat exchanger has a tank, plural exhaust gas tubes provided in the tank through which exhaust gas flows. A water passage is defined in the tank where cooling water flows from a cooling water inlet pipe to a cooling water outlet pipe. The plurality of exhaust gas tubes are connected to core plates at an upstream side thereof and a downstream side thereof. The core plates are connected to bonnets at both sides of the tank. A peripheral portion of at least one of the core plates is folded toward the bonnet to which said at least one of the core plates is connected.
With this feature, the cooling water inlet pipe, for example, can be disposed close to the core plate at the upstream side. In this case, the cooling water can flow close to the upstream side of the plural exhaust gas tubes. As a result, the cooling water can be prevented from being stuck at the upstream side of plural exhaust gas tubes.
Preferably, the at least one of the core plates is the one disposed at the upstream side of the plural exhaust gas tubes.
Preferably, the cooling water inlet pipe or the cooling water outlet pipe is disposed on the tank at a location where the disposed distance of the pipe from the core plate is equal to or less than a diameter of the pipe.
Other features and advantages of the resent invention will become more apparent from the following detailed description made with reference to the accompanying drawings.